This invention relates to an improved hatch cover for railroad hopper cars and to a novel method of constructing the hatch cover.
The hatch covers that are presently used to cover open-topped railroad hopper cars suffer from numerous problems, perhaps the most important of which is their susceptibility to damage when treated roughly. Existing hatch covers are typically formed in a compression molding process wherein a charge of molding compound is placed in an open mold. The mold is closed on the molding compound, and heat and pressure are applied, usually in the range of 225.degree. F. to 320.degree. F. and 150 to 2000 PSI. The curing time typically ranges from less than 1 minute to about 5 minutes, depending on the thickness, size and shape of the part, and the finished part is removed after the mold has been opened.
The need for high temperatures and pressures in the molding process leads to relatively high cost and to other obvious problems. The molding compound does not readily flow into deep ribs and bosses, and the reduced reinforcement and decreased stiffening effect provided by the imperfect ribs detracts from their effectiveness in strengthening the hatch cover. In addition, the molding process often causes variations in part thickness, and relatively large parts such as hatch covers experience drastic shrinkage and warpage problems when thickness variations are present. As a result, the hatch cover often has one or more weakened areas which are highly susceptible to damage when the cover is handled roughly or otherwise abused in the field. It is not uncommon for the hatch cover to be slammed open in a forceful manner and walked on when in the open position. The areas most susceptible to damage are at the perimeter of the hatch cover and at the hinge area where the forces are concentrated when the cover is treated roughly. The bumpers which serve to prevent damage to the main panel of the hatch cover are also frequently damaged.